Methods and apparatus for network energy savings in a wireless communication system

ABSTRACT

Disclosed herein are methods and apparatus for network energy savings in a wireless communication system, such as the 3GPP LTE system. Particularly, one such method reduces power consumption in a base station by selectively muting or disabling downlink transmissions of certain control signal symbols in one or more subframes or frames. The disclosed methods and apparatus can apply independently or in combination in both FDD and TDD systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/305,071 filed on Feb. 16, 2010, entitled “Methods and Systems forNetwork Energy Saving in Wireless Communication Systems,” the contentsof which are incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to Energy Saving (ES) managementin the network infrastructure of wireless communication systems, andmore particularly to methods and apparatus for reducing powerconsumption in downlink transmissions in the 3rd Generation PartnershipProject (3GPP) Long-term Evolution (LTE) wireless communication systemsusing frequency division duplex (FDD) and time division duplex (TDD).

BACKGROUND

Energy saving and power reduction have been and will continue to be anarea of prime interest in the wireless communication community. Almostevery mobile device manufacturer and provider is required to implementand incorporate into their mobile terminal products power-savingtechniques as required under the wireless communication standards, suchas the mandatory features of handset discontinuous transmission (DTX)and reception (DRX) that can help improve the battery life in mobileproducts. Most mobile network operators or carriers are also faced withstrong requirements to reduce their greenhouse emissions and energyconsumption as they keep building out and maintaining the networkinfrastructure in order to provide better wireless communicationservices to customers. In recent years, the deployment of networkequipment on a massive scale has led to a steady increase in pollutionand energy consumption worldwide. Particularly in emerging markets wherebasic infrastructure elements, such as electricity grids andconnections, are often underdeveloped, there is even higher energyconsumption due to the network operator's use of conventional equipmentssuch as diesel generators in building cell towers and base stationsites. As a result, many authorities ranging from local governments tointernational organizations have formulated and are enforcingenvironmental requirements that mobile network operators need to complywith. Energy Saving (ES) mechanisms are becoming an integral part of thenew generation radio access networks such as LTE, and consequently, ofmost wireless communication systems. A good ES solution needs to ensureno service degradation or inefficiencies in the network. This means,backward compatibility should be fully considered in designing an ESscheme, especially in networks that serve a number of legacy userequipments (UEs).

A large part of the network energy consumption is attributed by thepower usage in base stations of a wireless communication network. Inaddition to power consumed for active cooling, different base stationcomponents, whether in a receiver or transmitter, need power to performbaseband processing, signal processing and many other computing tasks.In particular, the RF components in a base station, mainly the poweramplifier (PA) in a transmitter, consume large amounts of power. Part ofthe power transmitted from an antenna can be lost in the PA. Sometimesthe PA efficiency (defined as a ratio between the PA output power andinput power) can be less than 50%. Such power loss can only be avoidedby temporarily turning off the PA. Therefore, determining how to reducepower loss and consumption in a PA can be crucial to the overall energyefficiency in a base station, which ultimately can significantlycontribute to the network energy savings in the entire wirelesscommunication system.

SUMMARY OF THE INVENTION

The disclosed exemplary embodiments are directed to solving issuesrelating to one or more of the problems presented in the prior art, aswell as providing additional features that will become readily apparentby reference to the following detailed description when taken inconjunction with the accompanying drawings.

One embodiment is directed to a method for energy savings in a wirelessnetwork. This method reduces downlink transmissions of a referencesignal by selectively muting reference signal symbols in a plurality ofsubframes of a frame in accordance with an energy saving (ES) scheme,each subframe divided into a first region and a second region, whereinthe ES scheme is configured to select from the plurality of subframes afirst set of subframes having reference signal symbols transmitted intheir first region and a second set of subframes having referencesymbols transmitted in their second region. Under the ES scheme, themethod further comprises one or more of the following: disablingtransmissions of reference signal symbols in the first region of allother subframes outside the first set of subframes; identifyingsubframes outside the second set of subframes; excluding subframes thatcarry at least a content signal symbol from the identified subframes todetermine remaining subframes; and disabling transmissions of referencesignal symbols in the second region of the remaining subframes. In oneembodiment, the wireless communication system is configured to providedownlink transmissions of a content signal according to a repetitionpattern, and the ES scheme is configured to modify or cancel therepetition pattern for downlink transmitting the content signal.

Another embodiment is directed to a method for reducing powerconsumption in downlink transmissions of one or more frames in awireless communication system, wherein each frame comprises a pluralityof subframes and each subframe is divided into at least a first regionand a second region in a time domain. This method comprises thefollowing: selecting a first group of subframes from the plurality ofsubframes, each of the first group of subframes having at least acontrol signal symbol in the first region; for each subframe notselected in the first group, disabling transmission of any controlsignal symbol in the first region; selecting a second group of subframesfrom the plurality of subframes, each of the second group of subframeshaving one or more control signal symbols in the second region; and foreach subframe not selected in the second group, disabling transmissionof any symbol in the second region unless the subframe carries aparticular content signal.

Yet another embodiment provides an apparatus for reducing powerconsumption in downlink transmissions of one or more frames in awireless communication system, wherein each frame comprises a pluralityof subframes and each subframe is divided into at least a first regionand a second region in a time domain. Such an apparatus comprises: meansfor selecting a first group of subframes from the plurality ofsubframes, each of the first group of subframes having at least acontrol signal symbol in the first region; means for disablingtransmission of any control signal symbol in the first region of eachsubframe not selected in the first group; means for selecting a secondgroup of subframes from the plurality of subframes, each of the secondgroup of subframes having one or more control signal symbols in thesecond region; and means for disabling transmission of any symbol in thesecond region unless the subframe carries a particular content signal ineach subframe not selected in the second group.

An alternative embodiment is directed to a computer program product forreducing power consumption in downlink transmissions of one or moreframes in a wireless communication system, wherein each frame comprisesa plurality of subframes and each subframe is divided into at least afirst region and a second region. The computer program product isembodied in computer-readable storage medium comprising instructions,while executed, causing a computer to perform: selecting a first groupof subframes from the plurality of subframes, each of the first group ofsubframes having at least a control signal symbol in the first region;for each subframe not selected in the first group, disablingtransmission of any control signal symbol in the first region; selectinga second group of subframes from the plurality of subframes, each of thesecond group of subframes having one or more control signal symbols inthe second region; and for each subframe not selected in the secondgroup, disabling transmission of any symbol in the second region unlessthe subframe carries a particular content signal.

Also, there is an embodiment providing a base station in a wirelesscommunication system, which comprises a transmitter configured fordownlink transmissions of a frame comprising a plurality of subframes,each subframe being divided into at least a first region and a secondregion; a downlink signal processor coupled to the transmitter; and acontroller coupled to the downlink signal processor, the controllercomprising a power reduction module configured to selectively disabledownlink transmissions of control signal symbols by: selecting a firstgroup of subframes from a plurality of subframes, each of the firstgroup of subframes having at least a control signal symbol in the firstregion; for each subframe not selected in the first group, disablingtransmission of any control signal symbol in the first region; selectinga second group of subframes from the plurality of subframes, each of thesecond group of subframes having one or more control signal symbols inthe second region; and for each subframe not selected in the secondgroup, disabling transmission of any symbol in the second region unlessthe subframe carries a particular content signal. The transmitter in thebase station is coupled to one or more power amplifiers (PAs), and thePA-on time in each PA is reduced by the power reduction module.

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments of the presentdisclosure, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments are described in detail with reference tothe following figures. The drawings are provided for purposes ofillustration only and merely depict exemplary embodiments of thedisclosure. These drawings are provided to facilitate the reader'sunderstanding of the invention and should not be considered limiting ofthe breadth, scope, or applicability of the disclosure. It should benoted that for clarity and ease of illustration these drawings are notnecessarily drawn to scale.

FIG. 1 is a simplified functional block diagram showing an exemplarywireless communication system for implementing embodiments of theinvention;

FIG. 2 shows an exemplary resource block that comprises subcarriers in afrequency domain and time symbols in a time domain according to anembodiment;

FIGS. 3 a-b show an exemplary downlink transmission and PA-on timedistribution per frame with full backward compatibility according to anembodiment;

FIGS. 4 a-b show an exemplary downlink transmission and PA-on timedistribution per frame under a maximized ES scheme according to anembodiment;

FIGS. 5 a-b show an exemplary downlink transmission and PA-on timedistribution per frame under a first ES scheme according to anembodiment;

FIGS. 6 a-b show an exemplary downlink transmission and PA-on timedistribution per frame under a second ES scheme according to anembodiment;

FIGS. 7 a-b show an exemplary downlink transmission and PA-on timedistribution per frame under a third ES scheme according to anembodiment;

FIG. 8 is a flow diagram illustrating an exemplary algorithm forreducing power consumption in downlink transmissions according to anembodiment; and

FIG. 9 is a simplified functional block diagram of an exemplary basestation in which embodiments of the invention can be implemented.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description is presented to enable a person of ordinaryskill in the art to make and use the invention. Descriptions of specificdevices, techniques, and applications are provided only as examples.Various modifications to the examples described herein will be readilyapparent to those of ordinary skill in the art, and the generalprinciples defined herein may be applied to other examples andapplications without departing from the spirit and scope of theinvention. Thus, the present invention is not intended to be limited tothe examples described herein and shown, but is to be accorded the scopeconsistent with the claims.

Reference will now be made in detail to aspects of the subjecttechnology, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

It should be understood that the specific order or hierarchy of steps inthe processes disclosed herein is an example of exemplary approaches.Based upon design preferences, it is understood that the specific orderor hierarchy of steps in the processes may be rearranged while remainingwithin the scope of the present disclosure. The accompanying methodclaims present elements of the various steps in a sample order, and arenot meant to be limited to the specific order or hierarchy presented.

Embodiments disclosed herein are directed to methods and apparatus fornetwork energy savings in a wireless communication system, such as the3GPP LTE system. These ES methods, schemes and solutions, whetherindependently or in combination, can be applied to a wirelesscommunication system configured to include both FDD and TDD systems.More specifically, various ES schemes will be described in terms of howto reduce power consumption (e.g., the fraction of PA-on time) indownlink transmissions in a base station without significant compromisesin backward compatibility. It should be appreciated that the embodimentsdescribed herein are based on 3GPP LTE specification by referring to theterms and concepts therein (e.g., CRS, PBCH, SIB1, PDCCH, PDSCH, frames,subframes, RE, RB, symbols, etc.), the application of these embodimentsare not so limited, but can include any wireless communication systemsusing different standards other than LTE.

FIG. 1 is a simplified functional block diagram of an exemplary wirelesscommunication system 100 in which embodiments for energy savings can beimplemented. The wireless communication system 100 includes a pluralityof base stations, such as base stations 110 a, 110 b, each supporting acorresponding service or coverage area 112 a, 112 b. The base stationsare capable of communicating with wireless devices within their coverageareas. For example, the first base station 110 a is capable ofwirelessly communicating with a first subscriber or client station 120 aand a second subscriber or client station 120 b within the coverage area112 a. Typically, the communications between a base station and a clientstation are supported by a modulation and/or repeat-coding schemedepending on various factors, such as QoS level of the client station,location or environment in which the client station operates. Forexample, the first base station 110 a can use one type of modulation andrepeat-coding scheme in communicating with the client station 120 a,while another type of modulation and repeat-coding scheme incommunicating with the client station 120 b. As shown in FIG. 1, thefirst client station 120 a is also within coverage area 112 b and iscapable of communicating with the second base station 110 b.

In this description, the communications path from the base station tothe client station is referred to as a downlink 116 a and thecommunications path from the client station to the base station isreferred to as an uplink 116 b. On both downlink and uplink, the radiosignal transmissions over the time are divided into periodic frames (orsubframes, slots, etc). Each radio frame contains multiple time symbolsthat include data symbols (DS) and reference symbols (RS). Data symbolscarry the data information, while the reference symbols are known atboth transmitter and receiver, and are used for channel estimationpurposes.

Although for simplicity only two base stations are shown in FIG. 1, atypical wireless communication system includes a much larger number ofbase stations. In a typical wireless communication system, the basestations 110 a and 110 b also communicate with each other over abackhaul network 130. The backhaul network 130 may include wired andwireless communications links, as well as supervisory network entities.The base stations 110 a and 110 b can also be configured as gateways,access points, radio frequency (RF) repeaters, frame repeaters or nodesand include any wireless network entry point.

The base stations 110 a and 110 b can be configured to support anomni-directional coverage area or a sectored coverage area. For example,the second base station 110 b is depicted as supporting a sectoredcoverage area 112 b. The coverage area 112 b is depicted as having threesectors, 114 a, 114 b, and 114 c, each of which can also be referred toas a coverage area. In typical embodiments, the second base station 110b treats each sector, for example sector 114 a, as effectively adistinct coverage area.

Although only two subscriber or client stations 120 a and 120 b areshown in the wireless communication system 100, typical systems areconfigured to support a large number of client stations. The clientstations 120 a and 120 b can be mobile, nomadic or stationary units. Theclient stations 120 a and 120 b are often referred to as, for example,mobile stations, mobile units, subscriber stations, wireless terminalsor the like. A client station can be, for example, a wireless handhelddevice, a vehicle mounted device, a portable device, client-premiseequipment, a fixed-location device, a wireless plug-in accessory or thelike. In some cases, a client station can take the form of a handheldcomputer, a notebook computer, a wireless telephone, a personal digitalassistant, a wireless email device, a personal media player,meter-reading equipment or the like.

In one embodiment, the wireless communication system 100 is configuredto comprise both FDD and TDD systems. Different communication techniquessuch as Orthogonal Frequency Division (OFDM) can be implemented in thewireless communication systems. The wireless communication system 100can also be configured to substantially comply with a standard systemspecification, such Long Term Evolution (LTE), or it may be aproprietary system. The embodiments described herein are not limited toapplication to LTE systems. The description in the context of an LTEsystem is offered for the purposes of providing a particular exampleonly.

In general, from the perspective of the standard specification, such asthe LTE standard (e.g., LTE Rel-10), most energy saving (ES) solutionscan be classified into three categories: ES in the time domain, ES inthe frequency domain and ES in the spatial domain. The ES solutions fromdifferent categories can be used independently or in combination. Forillustration purposes only, the following paragraphs will describe a fewES solutions in each category.

1. ES Solutions in Frequency Domain

For energy saving purposes, bandwidth split and shrinking can helpreduce transmission power. However, if a power amplifier (PA) isconfigured to operate at an optimized level of output power, a furtherreduced output power can compromise the PA efficiency. In that case, thetotal energy savings in PA can be marginal and undesirable.Additionally, reducing bandwidth in exchange for saving energyconsumption may constrain the network operator's service capability inlow-traffic areas where user traffic can be unpredictable and highlydependent upon the available bandwidth. For example, to make anemergency call with positioning services may need a large systembandwidth in the LTE system.

Another ES solution in the frequency domain can be used in the case ofcarrier aggregation. If each carrier to be aggregated has a separate PAattached thereto, when the carriers are aggregated, their attached PAcan be turned off to save power. However, this solution may not beapplicable for contiguous aggregated carriers that are supported by asingle PA. Although most ES solutions in the frequency domain can beapplied independently or jointly, their overall effectiveness can belimited.

2. ES Solutions in Spatial Domain

Because each antenna port in a base station has its own PA, one directES solution in the spatial domain is to reduce the number of antennaports and their associated PAs. However, this solution reduces powerconsumption at the cost of cell coverage. As an example, in a 2-by-2port configuration for transmit diversity, if the antenna ports arereduced from 2 to 1, there will be at least a 3 dB loss on link gain.Under the urban-micro NLOS pathloss model given by 3GPP for a hexagonalcell, which is defined by

PL=36.7 log₁₀(d)+22.7+26 log₁₀(f_(c)) (Antenna height being 10 m)

the 3 dB loss on link gain can be translated into a much smaller cellcoverage, with a new cell's radius reduced to 10̂(−3/36.7)=82.8% of theoriginal cell. The resulting “coverage holes” will certainly interferewith the quality of service by network operators in their advertisedcoverage area. In order to seal the coverage holes, the network operatorcan increase the transmission power in each cell, which, however,defeats the purpose of this ES solution by reducing antenna ports.

An alternative spatial domain ES solution is to partially switch offcertain cells and increase transmission powers in the remaining cells tokeep full cell coverage. However, sometimes the required power increasein the remaining cells can out weigh the power savings from switchingoff cells. For example, in a 2-D hexagonal cell layout in anurban-micro, if every other cell on both X-axis and Y-axis is switchedoff, that means, a total ¾ of the cells are switched off. In order toretain the full coverage, the radius of remaining cells needs to bedoubled. This requires the transmission power of each remaining cell toincrease to 10̂(36.7 log₁₀(2)/10)=12.7 times of the original power. Ifthe transmission power of each remaining cell stays the same, increasingthe base station antenna height in the remaining active cells can alsohelp keep the full cell coverage. However, to increase the antennaheight can be practically difficult and costly, and sometimes not evenfeasible due to local regulations. Considering the cell coverage loss,these spatial domain ES solutions may not be effective enough in actualnetwork operations.

3. ES Solutions in Time Domain

A common goal among the ES solutions in the time domain is to reduce thefraction of downlink transmission time or PA-on time, namely, the timeduration in which downlink transmissions take place. By reducing thePA-on time, a PA can consume less power and achieve energy savings inthe base station.

In the 3GPP LTE system, the transmission time is partitioned into 10ms-long frames. Each frame is further equally divided into 10 subframes,typically labeled as SF #0, SF #1, SF #2 . . . and SF #9. FIG. 2 showsan exemplary resource block (RB) 200 according to one specific systemconfiguration (called normal cyclic prefix, or normal-CP) in LTEsystems. As seen in FIG. 2, one subframe contains 14 equally-dividedtime slots or symbols 202 in the time domain, usually labeled as l=0, 1,2, 3 . . . 12, 13. Also, a regular subframe is typically partitionedinto two parts: a physical downlink control channel (PDCCH) 230 and aphysical downlink shared channel (PDSCH) 240. The PDCCH region 230normally occupies the first few symbols at the start of a subframe andcarries user-specific control channels, and the PDSCH region 240typically occupies the remaining symbols the subframe and carriesgeneral-purpose traffic. Besides the time symbols 202 in the timedomain, the RB 200 in FIG. 2 is also defined by the bandwidth in thefrequency domain, which is equally divided into 12 subcarriers 201. Assuch, one resource block is defined over a rectangular two-dimensional(2-D) or frequency-time resource area, and more specifically, it covers12 contiguous subcarriers in the frequency domain and one subframe or 14time symbols in the time domain, as shown in FIG. 2. Each resource blockcomprises a plurality of resource elements (RE) and each RE is definedby single units in the frequency and time domains. For example, a RE 210or 220 in FIG. 2 is defined by a symbol in the time domain and asubcarrier in the frequency domain. In the following description, anotation <subframe_index; symbol_indices> will be used to show a signallocation in the time domain, where subframe_index is a subframe index ina frame and symbol_indices mean one or more symbol index in the indexedsubframe.

The PA-on time can be minimized if the transmission management unit orscheduler in a base station can schedule downlink transmissions to theextent that, for a certain period of time duration (e.g., a frame, asubframe or a few symbols or time units), there is no downlink traffic(voice or data) transmission. In theory, this can be achieved in a lowtraffic load cell in a 3G/4G wireless system. In reality, however, evenin the absence of any user traffic, a base station still needs totransmit at least some mandatory common signals, i.e., signals broadcastthroughout a cell that the base station serves. Under the LTE standardspecification, the following downlink transmissions are required to stayactive even in case of zero-load of user traffic.

a. Primary Synchronization Signal (PSS) and Secondary SynchronizationSignal (SSS)

These two signals are used for the initial synchronization and detectionof any cell identification after a mobile or client device is poweredup. Their transmissions are usually required to repeat in every frame.In a normal-CP system configuration, the transmission of PSS occurs attime locations of <0; 6> and <5; 6> in the FDD system. In other words,within each frame, PSS downlink transmission occurs at symbol 6 of twosubframes, subframe #0 and subframe #5. For the TDD system, PSStransmission occurs at time locations of <1; 2> and <6; 2>. Thetransmission of SSS occurs at time locations of <0; 5> and <5; 5> forthe FDD system, and time locations of <0; 13> and <5; 13> for TDD. Thetransmission of PSS and SSS will be further explained later withreference to FIGS. 3 a-b, 4 a-b, 5 a-b, 6 a-6 b and 7 a-b.

b. Physical Broadcast Channel (PBCH)

PBCH is used for broadcasting essential cell information to mobiledevices or clients within a cell. PBCH transmission also repeats in eachframe, and usually occurs at time locations of <0; 7˜10>. This means,PBCH is transmitted over time symbols 7-10 in subframe #0.

c. Cell-specific Reference Signal (CRS)

CRS is often used for downlink signal strength measurement. It is alsoused for coherent demodulation of PDSCH in the same resource block.Sometimes it can be used for verification of cell identification done onPSS and SSS. CRS transmissions have the same pattern in each regularsubframe. For example, in case of two transmission antenna ports, theCRS transmission occurs at time locations of <*; 0, 4, 7, 11>, where *represents any regular subframe in the normal-CP configuration.Referring back to FIG. 2, in one resource block, CRS transmission forone antenna port covers two subcarriers in the frequency domain, forexample, two R₀ (CRS for antenna port 0) and two R₁ (CRS for antennaport 1). Also, as seen in FIG. 2, CRS transmission covers symbols 0, 4,7 and 11 in the time domain. It should be noted that, the CRS symbol 0is transmitted within the PDCCH region 230, and all other CRS symbols 4,7 and 11 are in the PDSCH region 240.

d. System Information Block (SIB)

SIB is the broadcast information that is not transmitted over PBCH. SIBis usually carried in specific PDSCH to be decoded by every handset ormobile device. This is because the capacity of PBCH is very limitedcompared to the total system information size. Therefore, a largeportion of system information is transmitted over the PDSCH with aspecial identity (S-RNTI) carried in an associated scheduling signal onthe PDCCH. Every handset checks the PDCCH with S-RNTI to receive thecomplete system information. There are multiple types of SIB in LTEsystems, most of which have a configurable longer transmission cycleexcept SIB type-1 (SIB1). SIB1 is usually fix-scheduled for transmissionin subframe #5 in every even frame, and its content is refreshed onceevery eight (8) frames. This means, the SIB1 content can be repetitivelytransmitted over a certain time cycle. As will be described later, tocancel or reduce such repetition of SIB1 transmissions can help cut downthe PA-on time and achieve energy savings.

Besides a regular subframe that contains 14 symbols in the time domain,which is typically partitioned into PDCCH and PDSCH regions as describedabove, the LTE specification also defines the following two types ofsubframes: MBSFN subframe and a special subframe. As will be explainedin detail below, the transmission of these two subframes can alsocontribute to the ES solutions in the time domain.

MBSFN subframe is a subframe that is defined to have the PDSCH regionreserved for MBMS (Multicast Broadcast Multimedia Service) traffic. Inother words, the MBSFN subframe excludes regular data traffic and CRSfrom its PDSCH region. Because of such configuration, a base station canuse MBSFN subframes to identify a zero-transmission region so that ahandset device or mobile station does not need to search for CRS withinthis region. Typically, the subframes {1, 2, 3, 6, 7, 8} are configuredas MBSFN subframes in FDD systems, and the subframes {3, 4, 7, 8, 9} areconfigured as MBSFN subframes in TDD systems. It should be noted thatMBSFN subframe has only one CRS symbol, i.e., symbol #0, and thisfeature can be considered for purposes of energy savings.

A special subframe is defined for TDD systems only. This subframe isused for downlink-to-uplink transition in the TDD system. The firstseveral symbols of a special subframe (minimum to 3 symbols, calledDwPTS) are used for downlink transmission, while the last severalsymbols (called UpPTS) are used for uplink transmission. For energysaving purposes, a minimum of three (3) symbols are adopted for downlinktransmission, in which case, there is only one CRS symbol in the specialsubframe. The special subframe is usually configured in subframe #1, andalso in subframe #6 for some special TDD allocation configurations. Asshown in Table 1 below, subframe #1 is configured as a special subframefor all TDD allocations from 0 to 6, while subframe 6 is configured as aspecial subframe for select TDD allocations including allocation 0, 1, 2and 6, but configured for downlink transmission for TDD allocations 3, 4and 5.

TABLE 1 TDD allocation configurations Uplink- Downlink- downlinkto-Uplink config- Switch-point Subframe number uration periodicity 0 1 23 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 2 5ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U D DD D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D

Among the time domain ES solutions currently considered in 3GPP LTEstudy, some ensure full backward compatibility, while others not. In thelatter case, there are certain concerns regarding the partial or zerobackward compatibility that need to be addressed in the proposed ESsolution.

In order to maintain full backward compatibility, all mandatory downlinksignals should be transmitted as required under the standards, and theMBSFN subframes should be used at the maximum. An exemplary downlinktransmission and PA-on time distribution per frame with full backwardcompatibility is presented in FIGS. 3 a-b. For illustration purposes,the following analysis of PA-on time is based on the assumption that theramp-up time for a PA is a half symbol and the ramp-down time is almostzero. This means, from the time point to turn on a PA and transmit anumber of (n) symbols to the time point of turning off the PA, the totalPA-on time is n+0.5 symbols.

FIG. 3 a illustrates an exemplary downlink transmission and timedistribution per frame with full backward compatibility in the FDDsystem 300 a. The frame 301 a comprises 10 subframes 302 a including SF#1, SF #2 . . . SF #9. Each subframe is partitioned into the PDCCHregion 303 a and the PDSCH region 304 a. As shown in FIG. 3 a, the PDCCHregion 303 a covers symbols 0, 1 and 2, while the PDSCH region coversthe remaining symbols 3, 4 . . . 12, 13. The transmission of eachsubframe in the time domain is demonstrated in time distributions 310 a,320 a, 330 a and 340 a. For instance, as shown in time distribution 310a, the downlink transmission of subframe #0 comprises transmitting 4 CRSsymbols {0, 4, 7, 11}, 4 PBCH symbols {7, 8, 9, 10} and 2 PSS/SSSsymbols {5, 6}. In this transmission, there are two PA ramp-ups thatoccur right before the transmission of the CRS symbol 0 and thetransmission of CRS symbol 4, respectively. As a result, the PA-on timecovers 8 symbols {0, 4˜11} plus two half symbols as ramp-up time, whichin sum is 10 symbols. Time distribution 320 a shows that subframe #5 isused for SIB1 transmission in an even frame, which takes a total of 14.5symbols. In an odd frame, subframe #5 is configured to comprise 4 CRSsymbols {0, 4, 7, 11} and 2 PSS/SSS symbols {5, 6}. In that regard, thePA-on time covers symbols {0, 4˜7, 11} plus three half symbols forramp-up, which in sum is 7.5 symbols. In other words, for subframe #5,there is 50% chance of 14.5 symbols and 50% chance of 7.5 symbols in thePA-on time. For subframes {4, 9}, time distribution 330 a shows theirdownlink transmissions include 4 CRS symbols {0, 4, 7, 11}. Thus, thePA-on covers symbols {0, 4, 7, 11} plus 4 half symbols for ramp-up,which is a total of 6 symbols. As shown in time distribution 340 a, allother downlink subframes {1, 2, 3, 6, 7, 8} are configured as MBSFNsubframes containing only one CRS symbol {0}. The resulting total PA-ontime is 1.5 symbols for each of these subframes. One exception issubframe #6, which, in even frames, does not need the half-symbolrump-up time due to a previously-continuous transmission of SIB1 insubframe #5, and thus has a different PA-on time of 1 symbol.

FIG. 3 b illustrates an exemplary downlink transmission and timedistribution per frame with full backward compatibility in the TDDsystem 300 b. As shown in time distribution 310 b, a downlinktransmission of subframe #0 in the time domain comprises 4 CRS symbols{0, 4, 7, 11}, 4 PBCH symbols {7, 8, 9, 10} and 1 SSS symbol {13}. Assuch, the PA-on time for subframe #0 covers symbols {0, 4, 7-11, 13}plus 4 half symbols as ramp-up time, which in sum is 10 symbols. Timedistribution 320 b shows that subframe #5 is used for SIB1 transmissionin an even frame, which takes a total of 14.5 symbols. In an odd frame,subframe #5 is configured to comprise 4 CRS symbols {0, 4, 7, 11} and 1SSS symbol {13}. In that regard, the PA-on time covers symbols {0, 4, 7,11, 13} plus 5 half symbols for ramp-up, which in sum is 7.5 symbols. Asshown in time distribution 330 b, subframes {1, 6} are configured asspecial subframes to cover 1 CRS symbol {0} and 1 PSS symbol {2}, whichresults in the total PA-on time of two symbols {0, 2} plus 1 half symbolfor ramp-up, a total of 2.5 symbols. But for certain TDD allocations(e.g., TDD allocations 3, 4 and 5 in Table 1), subframe #6 is configuredas a non-special downlink subframe, which includes 4 CRS symbols {0, 4,7, 11} and 1 PSS symbol {2}. In that configuration, the PA-on timecovers symbols {0, 2, 4, 7, 11} plus 4 half symbols for ramp-up, totaledto be 7 symbols. Other downlink subframes {3, 4, 7, 8, 9} are configuredas MBSFN subframes each comprising 1 CRS symbol {0}, as presented intime distribution 340 b. The PA-on time for each of these subframes is1.5 symbols.

Table 2 below shows PA-on time distributions with full backwardcompatibility for both FDD and TDD:

TABLE 2 PA-on time distribution w/full backward compatibility SubframePA-on 0 1 2 3 4 5 6 7 8 9 fraction TDD 0 10 2.5 — — — 14.5 in even 2.5 —— — 18.6% config- 1 — — 1.5 frame; 7.5 in — — 1.5 20.7% urations 2 — 1.51.5 odd frame — 1.5 1.5 22.3% 6 — — — — — 1.5 19.6% 3 — — — 7 1.5 1.51.5  25% 4 — — 1.5 1.5 1.5 1.5 26.1% 5 — 1.5 1.5 1.5 1.5 1.5 27.1% FDD10 1.5 1.5 1.5 6 14.5 in even 1.5 in even 1.5 1.5 6 29.8% frame; 7.5 inframe; 1 in odd frame odd frame

To minimize the PA-on time, one solution proposed by 3GPP RANI is tomute or disable the transmission of CRS as long as such muting ornon-transmission does not affect the reception of PBCH and SIB1. This ESsolution is referred as Maximum CRS-DTX in the following description. Anexemplary downlink transmission and PA-on time distribution per frameusing the Maximum CRS-DTX scheme is illustrated in FIGS. 4 a-4 b.

FIG. 4 a illustrates an exemplary downlink transmission and timedistribution per frame with Maximum CRS-DTX in the FDD system 400 a. Asshown in time distribution 410 a, the downlink transmission of subframe#0 comprises transmissions of 2 CRS symbols {7, 11}, 4 PBCH symbols {7,8, 9, 10} and 2 PSS/SSS symbols {5, 6}. The total PA-on time coverssymbols {5˜11} plus one half symbol as ramp-up time, which in sum is 7.5symbols. In comparison with the time distribution 310 a in FIG. 3 a,where full backward compatibility is provided, CRS symbols {0, 4} aremuted in time distribution 410 a for subframe #0, and thus the PA-ontime is reduced by 2.5 symbols. Time distribution 420 a shows thatsubframe #5 is used for SIB1 transmission in an even frame, which takesa total of 14.5 symbols. In an odd frame, subframe #5 is configured tocomprise 2 PSS/SSS symbols {5, 6}, with all CRS symbols {0, 4, 7, 11}being muted. This results in the PA-on time of two symbols plus one halfsymbol for PA rump-up, a total of 2.5 symbols. Thus, for subframe #5,there is 50% chance of 14.5 symbols and 50% chance of 2.5 symbols in thePA-on time. For all other downlink subframes {1, 2, 3, 4, 6, 7, 8, 9},as shown in time distributions 430 a and 440 a, there is zero PA-on timebecause all CRS symbols are muted.

FIG. 4 b illustrates an exemplary downlink transmission and timedistribution per frame with Maximum CRS-DTX in the TDD system 400 b.According to time distribution 410 b, subframe #0 comprises 2 CRSsymbols {7, 11}, 4 PBCH symbols {7, 8, 9, 10} and 1 SSS symbol {13}. Asa result, the PA-on time covers symbols {7-11, 13} plus 2 half symbolsfor ramp-up, which is a total of 7 symbols. Because CRS symbols {0, 4}are muted in subframe #0, the PA-on time is reduced from 10 symbols to 7symbols, if compared to the time distribution 310 b in FIG. 3 b. Timedistribution 420 b shows that subframe #5 is used for SIB1 transmissionin an even frame, which takes a total of 14.5 symbols. In an odd frame,subframe #5 is configured to comprise 1 SSS symbol {13}, with CRSsymbols {0, 4, 7, 11} not being transmitted, for which there is a totalof 1.5 symbols of PA-on time. As shown in time distribution 430 b,subframes {1, 6} are configured as special subframes to cover 1 PSSsymbol {2}, which results in 1.5 symbols of PA-on time. For certain TDDallocations (as described above in FIG. 3 b), subframe #6 is configuredas non-special subframe, which covers 1 PSS symbol {2} as shown in timedistribution 430 b. This results in a total of 1.5 symbols as the PA-ontime. For all other downlink subframes {3, 4, 7, 8, 9}, as shown in timedistribution 440 b, there is zero PA-on time because all CRS symbols aremuted.

Under the Maximum CRS-DTX scheme, the PA-on time can be reduced bymuting CRS symbols. However, if a large number of CRS symbols are nottransmitted, there will be little support for backward compatibility,which may cause many issues for legacy UEs in the LTE network. Table 3below includes some measurements showing the lack of backwardcompatibility, such as the number of remaining CRS REs and muted CRS REs(lost to legacy UE) per port per subframe. Note that N_(RB) ^(DL)denotes the bandwidth measured in the unit of RB.

TABLE 3 PA-on time distributions w/maximized CRS-DTX # of CRS RE # ofCRS RE per remaining per port per frame Subframe PA-on port per framelost to legacy UE 0 1 2 3 4 5 6 7 8 9 fraction (average) (average) TDD 07 1.5 — — — 14.5 in 1.5 — — — 12.9% 8N_(RB) ^(DL) 12N_(RB) ^(DL)allocations 1 — — 0 even frame; — — 0 16N_(RB) ^(DL) 2 — 0 0 1.5 in — 00 20N_(RB) ^(DL) 6 — — — odd frame — — 0 14N_(RB) ^(DL) 3 — — — 1.5 0 00 24N_(RB) ^(DL) 4 — — 0 0 0 0 26N_(RB) ^(DL) 5 — 0 0 0 0 0 28N_(RB)^(DL) FDD 7.5 0 0 0 0 14.5 in 0 0 0 0 11.4% 8N_(RB) ^(DL) 36N_(RB) ^(DL)even frame; 2.5 in odd frame

Alternative time domain ES solutions are needed to address the backwardcompatibility issues. In general, these ES solutions should aim atreducing the number of CRS symbols to be muted and providing a betterbalance between energy savings and backward compatibility in the LTEsystems. In other words, rather than muting most CRS symbols under theMaximum CRS-DTX solution, the alternative time domain ES solutions willselectively mute CRS symbols. So the question becomes, which CRS symbolsor how many CRS symbols should be muted. FIG. 8 presents an exemplaryalgorithm for determining the CRS symbols for no transmission in oneembodiment of the invention.

As shown in FIG. 8, the selectively-muting process 800 for determiningmuted or non-transmitted CRS symbols includes two subframe selections:selecting a set of subframes in which CRS symbols are transmitted in thePDCCH region of the subframe in step 810, and selecting a set ofsubframes in which CRS symbols are transmitted in the PDSCH region ofthe subframe in step 830. These two selections can be represented by thefollowing denotations:

-   -   Ψ_(PDCCH)={i}, where i is the index or indices of the selected        subframes in which CRS symbols are transmitted in the PDCCH        region;    -   Ψ_(PDSCH)={j}, where j is the index or indices of the selected        subframes in which CRS symbols are transmitted in the PDSCH        region.        For example, Ψ_(PDCCH)={0, 5} means subframe #0 and subframe #5        are the selected subframes in which at least a CRS symbol        (symbol 0) is transmitted in the PDCCH region. On the other        hand, Ψ_(PDSCH)={4, 9} means subframe #4 and subframe #9 are        selected subframes in which CRS symbols (e.g., symbols 4, 7, 11)        are transmitted in the PDSCH region.

After the subframes are selected, certain CRS symbols in thosenon-selected subframes may be muted or non-transmitted. Specifically, asshown in step 820, for subframes not selected in the first group (i.e.,subframes not belonging to Ψ_(PDCCH)), the CRS symbols in their PDCCHregions are muted. For subframes not selected in the second group (i.e.,subframes not belonging to Ψ_(PDSCH)); as explained at step 840, the CRSsymbols in their PDSCH regions to Ψ_(PDSCH) are muted if that subframedoes not carry either PBCH or PDSCH; otherwise the transmission of CRSsymbols in the PDSCH region stays on. Following the above example,Ψ_(PDCCH)={0, 5} means that the non-selected subframes or subframes notbelonging to Ψ_(PDCCH) are subframes {1-4, 6-9}, and the CRS symbol(symbol 0) in each of these subframes is muted. On the other hand,Ψ_(PDSCH)={4, 9} means that the non-selected subframes or subframes notbelonging to Ψ_(PDCCH) are subframes {0-3, 5-8}. For each of thesesubframes, the CRS symbols (symbols 4, 7, 11), if any, can be muted ifthe subframe does not carry PBCH or PDSCH. Because subframe #0 andsubframe #5 usually carry PBCH or SIB traffic, the CRS symbols (symbols4, 7, 11) in those frames are still transmitted.

Following the above-discussed CRS-muting algorithm, many possible ESschemes can be formulated depending on which subframes are selected inΨ_(PDCCH) and Ψ_(PDSCH), respectively. The following paragraphs willdescribe a few exemplary ES schemes implementing the above selectiveCRS-muting or CRS-DTX process.

CRS-DTX-Opt-1

Under this option, CRS is transmitted in the PDCCH region of everydownlink subframe, and CRS is muted in the PDSCH region in any subframehaving neither PBCH nor PDSCH. This means, Ψ_(PDCCH)={all downlinksubframes having PDCCH}, and Ψ_(PDSCH)=Ø. Note that the CRS symbolsfalling within the PDSCH region of subframes {0, 5} are stilltransmitted due to the presence of PBCH or SIB1 in those subframes.

CRS-DTX-Opt-2

Under this option, all CRS symbols, including symbols in both PDCCH andPDSCH regions, are transmitted in select subframes, for example,subframes {0, 5}. CRS symbols are muted in other subframes not carryingPBCH or PDSCH. This means, Ψ_(PDCCH)=Ψ_(PDSCH)={selected subframes},namely, subframes {0, 5} in this example.

CRS-DTX-Opt-3

This option transmits CRS in the PDSCH region to meet the minimumrequirement for demodulation of PBCH and SIB1, which means,Ψ_(PDSCH)={0, 5}. In addition, CRS in the PDCCH region is transmitted inthe subframes carrying PBCH or SIB1 and the subframes followingtransmission of PBCH or SIB1, which means, Ψ_(PDCCH)={0, 1, 5, 6}.

Another solution to further reduce the PA-on time without causingnegative impact upon the physical layer procedures in the LTE system isto cancel the repetition of SIB1 transmission. This solution is referredas No-SIB1-repetition in the following description. Given that thecontents of SIB1 are refreshed once every eight (8) frames, SIB1 doesnot need to be transmitted in every other frame but every one of eightframes. Its duty cycle is thus reduced from ½ to ⅛. The transmission ofSIB1 in each subframe remains the same as in the 3GPP LTE standardspecification. This solution can be used in combination with any one ofthe above CRS-muting options, which will be described in detail in thefollowing paragraphs with reference to FIGS. 5 a-b, 6 a-b and 7 a-b.

FIGS. 5 a-b illustrate an exemplary downlink transmission and PA-on timedistribution per frame under an ES scheme combining CRS-DTX-Opt-1 andNo-SIB1-repetition. Under this scheme, CRS symbols in the PDCCH regionof all subframes are transmitted, while CRS symbols in the PDSCH regionof all subframes are muted except for the subframes carrying PBCH orSIB1.

In the FDD system 500 a illustrated in FIG. 5 a, a downlink transmissionof subframe #0 is comprised of transmissions of 4 CRS symbols {0, 4, 7,11}, 4 PBCH symbols {7, 8, 9, 10}, 2 PSS/SSS symbols {5, 6} according totime distribution 510 a. As such, the PA-on time covers symbols {0,4˜11} plus 2 half symbols as ramp-up time, which in sum is 10 symbols.As shown in time distribution 520 a, subframe #5 in a frame sending SIB1is configured to cover 14.5 symbols for SIB1 traffic transmission. Whensubframe #5 is in a frame without SIB1, it is configured to cover oneCRS symbol {0}, 2 PSS/SSS symbols {5, 6}, which means the total PA-ontime covers symbols {0, 5˜6} plus 2 half symbols for ramp-up and totalsto be 4 symbols. Time distribution 520 a also shows that subframe #6 inthe frame sending SIB1 is configured to cover 1 CRS symbol {0} to betransmitted immediately after the transmission of SIB1 in subframe #5.Thus, no ramp-up time is needed in this configuration, and the totalPA-on time is 1 symbol. For subframe #6 in the frame not sending SIB1,it covers 1 CRS symbol {0} and the PA-on time is 1.5 symbols. As aresult, depending on whether the frame transmits SIB1, the total PA-ontime for transmissions of subframes {5, 6} can be 15.5 (=14.5+1) symbolsor 5.5 (˜4+1.5) symbols. With the No-SIB1-repetition solution,transmission of SIB1 occurs every one out of eight frames. Thus, thereis ⅛ chance of 15.5 symbols of PA-on time and ⅞ chance of 5.5 symbols ofPA-on time. Time distributions 530 a and 540 a show that all otherdownlink subframes are configured to carry 1 CRS symbol {0} with a totalof 1.5 symbols of PA-on time.

In the TDD system 500 b shown in FIG. 5 b, subframe #0 carries 4 CRSsymbols {0, 4, 7, 11}, 4 PBCH symbols {7, 8, 9, 10} and 1 SSS symbol{13} as shown in time distribution 510 b. That means, the PA-on timecovers {0, 4, 7-11, 13} plus 4 half symbols for ramp-up, resulting atotal of 10 symbols. Time distribution 520 b shows that subframe #5 in aframe sending SIB1 has PA-on time of 14.5 symbols, and if in a framecontaining no SIB1, the subframe #5 covers 1 CRS symbols {0} and 1 SSSsymbol {13}, resulting in the PA-on time covering symbols {0, 13} plus 2half symbols for ramp-up, a total of 3 symbols. With theNo-SIB1-repetition solution, there is ⅛ chance of 14.5 symbols of PA-ontime and ⅞ chance of 3 symbols of PA-on time for subframe #5. As shownin time distribution 530 b, subframes {1, 6} are configured as specialsubframes to cover 1 CRS symbol {0} and 1 PSS symbol {2}. That means,the PA-on time covers symbols {0, 2} plus 1 half symbol for ramp-up, atotal of 2.5 symbols. For certain TDD allocations, subframe #6 isconfigured as a non-special subframe, which carries 1 CRS symbols {0}and 1 PSS symbol {2}. In that configuration, the total PA-on time coverssymbols {0, 2} plus 1 half symbol for ramp-up, a total of 2.5 symbols.Time distribution 540 b shows all other downlink subframes {3, 4, 7, 8,9} are configured to cover 1 CRS symbol {0} with 1.5 symbols of PA-ontime.

Compared to the Maximum CRS-DTX scheme, the number of muted CRS symbolsunder this scheme is reduced, thereby leaving a larger number ofremaining CRS REs per port per frame for a better backwardcompatibility, as shown in Table 4 below:

TABLE 4 PA-on time distributions w/CRS-DTX-Opt-1 and No-SIB1-repeat # ofCRS RE # of CRS RE per remaining per port per frame Subframe PA-on portper frame lost to legacy UE 0 1 2 3 4 5 6 7 8 9 fraction (minimum)(maximum) TDD 0 10 2.5 — — — 14.5 w/1/8 2.5 — — — 13.9% 14N_(RB) ^(DL) 6N_(RB) ^(DL) allocations 1 — — 1.5 chance; — — 1.5  16% 18N_(RB) ^(DL)2 — 1.5 1.5 3 w/7/8 — 1.5 1.5 18.2% 22N_(RB) ^(DL) 6 — — — chance — —1.5  15% 16N_(RB) ^(DL) 3 — — — 2.5 1.5 1.5 1.5 17.1% 20N_(RB) ^(DL)12N_(RB) ^(DL) 4 — — 1.5 1.5 1.5 1.5 18.2% 22N_(RB) ^(DL) 5 — 1.5 1.51.5 1.5 1.5 19.2% 24N_(RB) ^(DL) FDD 10 1.5 1.5 1.5 1.5 15.5 for 1/8 1.51.5 1.5 19.5% 26N_(RB) ^(DL) 18N_(RB) ^(DL) chance; 5.5 for 7/8 chance

FIGS. 6 a-b illustrate an exemplary downlink transmission and PA-on timedistribution per frame under an ES scheme combining CRS-DTX-Opt-2 andNo-SIB1-repetition. Under this scheme, all CRS symbols, includingsymbols in both PDCCH and PDSCH regions, are transmitted in subframes{0, 5}, and CRS symbols are muted in other subframes {1-4, 6-9} unlessthe subframe carries PBCH or PDSCH.

In the FDD system 600 a illustrated in FIG. 6 a, time distribution 610 ashows that subframe #0 is configured to carry 4 CRS symbols {0, 4, 7,11}, 4 PBCH symbols {7, 8, 9, 10} and 2 PSS/SSS symbols {5, 6}. Thus,the PA-on time covers symbols {0, 4˜11} plus 2 half symbols for ramp-up,which in sum is 10 symbols. As shown in time distribution 620 a,subframe #5 in a frame containing SIB1 comprises 14.5 symbols in PA-ontime. In frames not sending SIB1; subframe #5 is configured to cover 4CRS symbol {0, 4, 7, 11} and 2 PSS/SSS symbols {5, 6}. That means, thePA-on time covers symbols {0, 4˜7, 11} plus 3 half symbols for ramp-up,a total of 7.5 symbols. With the No-SIB1-repetition solution, there is ⅛chance of 14.5 symbols of PA-on time and ⅞ chance of 7.5 symbols ofPA-on time for subframe #5. For all other subframes {1-4, 6-9}, timedistributions 630 a and 640 a show that there is zero PA-on time becauseall CRS symbols are muted.

In the TDD system 600 b illustrated in FIG. 6 b, time distribution 610 bshows that subframe #0 is configured to cover 4 CRS symbols {0, 4, 7,11}, 4 PBCH symbols {7, 8, 9, 10} and 1 SSS symbol {13}. In thisconfiguration, the PA-on time covers symbols {0, 4, 7-11, 13}, which isin sum 10 symbols. As shown in time distribution 620 b, subframe #5 isconfigured to cover 14.5 symbols in a frame containing SIB1. In theframe without SIB1; subframe #5 is configured to cover CRS symbols {0,4, 7, 11} and 1 SSS symbol {13}. In this configuration, the PA-on timeis a total of 7.5 symbols. With the No-SIB1-repetition solution, thereis ⅛ chance of 14.5 symbols of PA-on time and ⅞ chance of 7.5 symbols ofPA-on time for subframe #5. Time distribution 630 b shows that subframes{1, 6} are configured as special subframes that cover 1 PSS symbol {2},which results in the total PA-on time of 1.5 symbols. For certain TDDallocations, subframe #6 is configured as a non-special subframe thatcovers 1 PSS symbol {2}, with the PA-on time of 1.5 symbols. For allother downlink subframes, as shown in time distribution 640 b, there iszero PA-on time because all CRS symbols are muted.

Compared to the Maximum CRS-DTX solution, this ES scheme also reducesthe number of muted CRS symbols, thereby leaving a larger number ofremaining CRS REs per port per frame for a better backwardcompatibility, as shown in Table 5 below:

TABLE 5 PA-on time distributions w/CRS-DTX-Opt-2 and No-SIB1-repeat # ofCRS RE # of CRS RE per remaining per port per frame Subframe PA-on portper frame lost to legacy UE 0 1 2 3 4 5 6 7 8 9 fraction (minimum)(minimum) TDD 0 10 1.5 — — — 14.5 w/1/8 1.5 — — — 15.3% 16N_(RB) ^(DL) 4N_(RB) ^(DL) allocations 1 — — 0 chance; — — 0  8N_(RB) ^(DL) 2 — 0 07.5 w/7/8 — 0 0 12N_(RB) ^(DL) 6 — — — chance — — 0  6N_(RB) ^(DL) 3 — —— 1.5 0 0 0 16N_(RB) ^(DL) 4 — — 0 0 0 0 18N_(RB) ^(DL) 5 — 0 0 0 0 020N_(RB) ^(DL) FDD 10 0 0 0 0 0 0 0 0 13.1% 16N_(RB) ^(DL) 28N_(RB)^(DL)

FIGS. 7 a-b illustrate an exemplary downlink transmission and PA-on timedistribution per frame under an ES scheme combining CRS-DTX-Opt-3 andNo-SIB1-repetition. Under this scheme, the CRS symbols are transmittedin the PDSCH region of subframes {0, 5} in order to meet the minimumrequirement for demodulation of PBCH and SIB1. In addition, CRS in thePDCCH region is transmitted in the subframes {0, 1, 5, 6}.

In the FDD system 700 a illustrated in FIG. 7 a, time distribution 710 ashows that subframe #0 is configured to carry 4 CRS symbols {0, 4, 7,11}, 4 PBCH symbols {7, 8, 9, 10} and 2 PSS/SSS symbols {5, 6}. So thePA-on time covers symbols {0, 4˜11} plus 2 half symbols for ramp-up,resulting a total of 10 symbols. As shown in time distribution 720 a,subframe #5 covers 14.5 symbols for SIB1 transmission in a frame sendingSIB1. If in a frame without SIB1, subframe #5 carries 4 CRS symbol {0,4, 7, 11} and 2 PSS/SSS symbols {5, 6}, resulting in PA-on time coveringsymbols {0, 4˜7, 11} plus 3 half symbol for ramp-up, which is a total of7.5 symbols. Time distribution 720 a also shows that subframe #6 in theframe sending SIB1 is configured to cover 1 CRS symbol {0} to betransmitted immediately after the transmission of SIB1 in subframe #5.Thus, no ramp-up time is needed in this configuration, and the totalPA-on time is 1 symbol. For subframe #6 in the frame not sending SIB1,it covers 1 CRS symbol {0} and the PA-on time is 1.5 symbols. As aresult, depending on whether the frame transmits SIB1, the total PA-ontime for transmissions of subframes {5, 6} can be 15.5 (=14.5+1) symbolsor 9 (=7.5+1.5) symbols. With the No-SIB1-repetition solution,transmission of SIB1 occurs every one out of eight frames. Thus, thereis ⅛ chance of 15.5 symbols of PA-on time and ⅞ chance of 9 symbols ofPA-on time. Time distribution 740 a shows that in subframe #1, 1 CRSsymbol {0} is transmitted in the PDCCH region, which results in 1.5symbols of PA-on time. All other subframes {2, 3, 4, 7, 8, 9}, as seenin time distributions 730 a and 740 a, have zero PA-on time because allCRS symbols are muted in these frames.

In the TDD system 700 b illustrated in FIG. 7 b, time distribution 710 bshows subframe #0 carries 4 CRS symbols {0, 4, 7, 11}, 4 PBCH symbols{7, 8, 9, 10} and 1 SSS symbols {13}. That means the PA-on time coverssymbols {0, 4, 7˜11, 13} plus 4 half symbols for ramp-up, a total of 10symbols. Time distribution 720 b shows that subframe #5 has PA-time of14.5 symbols for in a frame sending SIB1. In a frame without SIB1, thesubframe #5 carries 4 CRS symbol {0, 4, 7, 11} and 1 SSS symbols {13},which results in PA-on time of 7.5 symbols. With the No-SIB1-repetitionsolution, there is ⅛ chance of 14.5 symbols of PA-on time and ⅞ chanceof 7.5 symbols of PA-on time for subframe #5. Time distribution 730 bshows subframes {1, 6} are configured as special subframes that have 1CRS symbol {0} and 1 PSS symbol {2}. In this configuration, the PA-ontime is two symbols {0, 2} plus 1 half symbol for ramp-up, a total of2.5 symbols. For certain TDD allocations, subframe #6 is configured as anon-special subframe, which covers 1 CRS symbol {0} and 1 PSS symbol{2}, with total PA-on of 2.5 symbols. Time distribution 740 b shows thatall other subframes {3, 4, 7, 8, 9} have zero PA-on time because all CRSsymbols are muted in these frames.

Compared to the Maximum CRS-DTX solution, this ES scheme reduces thenumber of muted CRS symbols while leaving a larger number of remainingCRS REs per port per frame for sufficient backward compatibility, asshown in Table 6 below:

TABLE 6 PA-on time distributions w/CRS-DTX-Opt-3 and No-SIB1-repeat # ofCRS RE # of CRS RE per remaining per port per frame Subframe PA-on portper frame lost to legacy UE 0 1 2 3 4 5 6 7 8 9 fraction (minimum)(minimum) TDD 0 10 2.5 — — — 14.5 w/1/8 2.5 — — — 16.7% 20N_(RB) ^(DL) 0allocations 1 — — 0 chance; — — 0  4N_(RB) ^(DL) 2 — 0 0 7.5 w/7/8 — 0 0 8N_(RB) ^(DL) 6 — — — chance — — 0  2N_(RB) ^(DL) 3 — — — 0 0 012N_(RB) ^(DL) 4 — — 0 0 0 0 14N_(RB) ^(DL) 5 — 0 0 0 0 0 16N_(RB) ^(DL)FDD 10 1.5 0 0 0 15.5 for 1/8 0 0 0 15.2% 20N_(RB) ^(DL) 24N_(RB) ^(DL)chance; 9 for 7/8 chance

It should be understood that the above ES schemes are for illustrationpurposes only, and depending on different choices of Ψ_(PDCCH) andΨ_(PDSCH), there can be many other possible CRS-muting or CRS-DTXconfigurations and implementations without departing from the spirit ofthe invention. For instance, choosing Ψ_(PDCCH)={1, 5, 6} andΨ_(PDSCH)={0, 5} can bring a different CRS-muting option as compared toCRS-DTX-Opt-3 as discussed above.

A further analysis of the data in the above Tables 2-6 suggests someadditional techniques can be employed for energy saving purposes. Forinstance, in TDD systems the TDD allocation #0 tends to have the minimalPA-on fraction no matter which specific subframes are selected inT_(PDCCH) and T_(PDSCH). In addition, TDD allocation #0 also tends tohave the least amount of CRS lost to legacy UE. This is because the TDDallocation #0 is usually an allocation of the least amount of downlinktransmission time. Accordingly, additional energy savings may beachieved if the TDD allocation can be adjusted dynamically to receivesimilar benefits as TDD allocation #0. To that end, however, the TDDallocation ratio may need frequent adjustments and in differentgeographical areas. This is can be practically difficult because asingle direct change in the TDD downlink-uplink allocation ratiotypically needs system-wide synchronization. This problem can be solvedby introducing some techniques that not only allow the TDD allocationratio to be changed asynchronously in a wireless system, but also enableusing different TDD allocation ratios in different geographical areas.These techniques are specified in select pending patent applications,including U.S. Provisional Application Ser. No. 61/027,412, filed Feb.8, 2008 and entitled “Dynamic Adjustment of Downlink/Uplink AllocationRatio in TDD Wireless Systems,” U.S. Provisional Patent Application No.61/039,072 filed on Mar. 24, 2008, entitled “Method for SignalingDownlink/Uplink Allocation Ratio Adjustment in LTE/TDD System,” U.S.Provisional Patent Application No. 61/138,896 filed Dec. 18, 2008,entitled “Method and System for Dynamic Adjustment of Downlink/UplinkAllocation Ratio in LTE/TDD System,” U.S. regular utility patentapplication Ser. No. 61/027,412 filed Feb. 6, 2009, entitled “DynamicAdjustment of Downlink/Uplink Allocation Ratio in TDD Wireless Systems,”U.S. regular utility patent application Ser. No. 61/039,072 filed Mar.24, 2009, entitled “Dynamic Adjustment and Signaling of Downlink/UplinkAllocation Ratio in LTE/TDD systems,” and U.S. provisional patentapplication Ser. No. 61/173,535 filed Apr. 28, 2009, entitled “Methodfor Live-Change of Downlink/Uplink Allocation Ratio in LTE/TDD System.”The contents of all these applications are incorporated herein byreference in their entirety.

Table 7 below provides a comparison of energy savings and backwardcompatibility among the above-described ES schemes using differentCRS-DTX solutions. In general, among all CRS-DTX methods for both FDDand TDD systems, the lower the PA-on fraction, the higher percentage ofCRS is lost to legacy UE. When it comes to each CRS-DTX method, however,one CRS-DTX method may provide a lower PA-on fraction in FDD systems butdoes not make a better solution for the TDD systems. Accordingly, inorder to achieve the best energy savings, FDD and TDD systems may beconfigured with different CRS-DTX methods and schemes.

TABLE 7 Comparison among different CRS-DTX methods FDD TDD PA-on % oflost PA-on % of lost CRS-DTX methods fraction CRS fraction CRSMax-CRS-DTX 8.21% 81.82% 9.38% 60% CRS-DTX-Opt-1 19.46% 40.91% 13.88% 30% CRS-DTX-Opt-2 13.13% 63.64% 15.27%  20% CRS-DTX-Opt-3 15.22% 54.55%16.7% 0 Full backward 27.81% 0 16.7% 0 compatibility

FIG. 9 is a simplified functional block diagram of an exemplary basestation 900 in which embodiments of the invention can be implemented.The base station 900 can be, for example, the first base station 110 ashown in the wireless communication system of FIG. 1. The base station900 includes the capabilities to configure and support the CRS-DTX orCRS-muting methods and different ES schemes according to variousembodiments of the invention. It should be noted that certain portionsof the base station 900 that operate to support the ES capabilities willbe described, while other portions of the base station 900 are omittedfor the purposes of brevity and clarity.

The base station 900 includes an antenna 902 coupled to an output of atransmitter 910 as well as to an input of a receiver 920. Thetransmitter 910 is couple to one or more power amplifiers (PA) 912 inwhich the power consumption can be reduced using the ES schemesdescribed herein. A downlink signal processor 930 is coupled to thetransmitter 910 for downlink transmission from the base station. Morespecifically, the DL signal processor 930 is typically coupled to aninput of one or more multiplexers (not shown) and the active multiplexerpath, as determined by a scheduler 960 coupled to the processor 930, iscoupled to the transmitter 910 for downlink transmission. The scheduler960, as a time management unit in the base station, is coupled to asystem clock 962. A controller 940 is coupled to the DL signal processor930. Typically, the controller 940 is configured to control theperformance of the base station by coordinating different computing andprocessing tasks. In one embodiment, the controller 940 is coupled to orconfigured with a power reduction module 942. The power reduction module942 can comprise computer codes and instructions implementing such analgorithm as shown in FIG. 8 for enabling different ES schemes usingCRS-DTX methods and many other techniques for power reduction. AnInput/Output administrative interface 950 is coupled to the controller940. It usually serves as an interface between the base station 900 andother network components or networks such as the backhaul network 130 inFIG. 1.

While various embodiments of the invention have been described above, itshould be understood that they have been presented by way of exampleonly, and not by way of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for thedisclosure, which is done to aid in understanding the features andfunctionality that can be included in the disclosure. The invention isnot restricted to the illustrated example architectures orconfigurations, but can be implemented using a variety of alternativearchitectures and configurations. Additionally, although the inventionis described above in terms of various exemplary embodiments andimplementations, it should be understood that the various features andfunctionality described in one or more of the individual embodiments arenot limited in their applicability to the particular embodiment withwhich they are described. They instead can be applied alone or in somecombination, to one or more of the other embodiments of the disclosure,whether or not such embodiments are described, and whether or not suchfeatures are presented as being a part of a described embodiment. Thusthe breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments.

In this document, the term “module” as used herein, refers to software,firmware, hardware, and any combination of these elements for performingthe associated functions described herein. Additionally, for purpose ofdiscussion, the various modules are described as discrete modules;however, as would be apparent to one of ordinary skill in the art, twoor more modules may be combined to form a single module that performsthe associated functions according embodiments of the invention.

In this document, the terms “computer program product”,“computer-readable medium”, and the like, may be used generally to referto media such as, memory storage devices, or storage unit. These, andother forms of computer-readable media, may be involved in storing oneor more instructions for use by processor to cause the processor toperform specified operations. Such instructions, generally referred toas “computer program code” (which may be grouped in the form of computerprograms or other groupings), when executed, enable the computingsystem.

It will be appreciated that, for clarity purposes, the above descriptionhas described embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits, processors or domains may be used without detracting from theinvention. For example, functionality illustrated to be performed byseparate processors or controllers may be performed by the sameprocessor or controller. Hence, references to specific functional unitsare only to be seen as references to suitable means for providing thedescribed functionality, rather than indicative of a strict logical orphysical structure or organization.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; and adjectivessuch as “conventional,” “traditional,” “normal,” “standard,” “known”,and terms of similar meaning, should not be construed as limiting theitem described to a given time period, or to an item available as of agiven time. But instead these terms should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable, known now, or at any time in the future. Likewise, a group ofitems linked with the conjunction “and” should not be read as requiringthat each and every one of those items be present in the grouping, butrather should be read as “and/or” unless expressly stated otherwise.Similarly, a group of items linked with the conjunction “or” should notbe read as requiring mutual exclusivity among that group, but rathershould also be read as “and/or” unless expressly stated otherwise.Furthermore, although items, elements or components of the invention maybe described or claimed in the singular, the plural is contemplated tobe within the scope thereof unless limitation to the singular isexplicitly stated. The presence of broadening words and phrases such as“one or more,” “at least,” “but not limited to”, or other like phrasesin some instances shall not be read to mean that the narrower case isintended or required in instances where such broadening phrases may beabsent.

Additionally, memory or other storage, as well as communicationcomponents, may be employed in embodiments of the invention. It will beappreciated that, for clarity purposes, the above description hasdescribed embodiments of the invention with reference to differentfunctional units and processors. However, it will be apparent that anysuitable distribution of functionality between different functionalunits, processing logic elements or domains may be used withoutdetracting from the invention. For example, functionality illustrated tobe performed by separate processing logic elements, or controllers, maybe performed by the same processing logic element, or controller. Hence,references to specific functional units are only to be seen asreferences to suitable means for providing the described functionality,rather than indicative of a strict logical or physical structure ororganization.

Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by, for example, a singleunit or processing logic element. Additionally, although individualfeatures may be included in different claims, these may possibly beadvantageously combined. The inclusion in different claims does notimply that a combination of features is not feasible and/oradvantageous. Also, the inclusion of a feature in one category of claimsdoes not imply a limitation to this category, but rather the feature maybe equally applicable to other claim categories, as appropriate.

What is claimed is:
 1. A method for energy savings in a wirelessnetwork, comprising: reducing downlink transmissions of a referencesignal by selectively muting reference signal symbols in a plurality ofsubframes of a frame in accordance with an energy saving (ES) scheme,each subframe divided into a first region and a second region, whereinthe ES scheme is configured to select from the plurality of subframes afirst set of subframes having reference signal symbols transmitted intheir first region and a second set of subframes having referencesymbols transmitted in their second region.
 2. The method of claim 1,further comprising: disabling transmissions of reference signal symbolsin the first region of all other subframes outside the first set ofsubframes in accordance with the ES scheme.
 3. The method of claim 1,further comprising: identifying subframes outside the second set ofsubframes; excluding subframes that carry at least a content signalsymbol from the identified subframes to determine remaining subframes;and disabling transmissions of reference signal symbols in the secondregion of the remaining subframes in accordance with the ES scheme. 4.The method of claim 1, wherein the wireless communication system isconfigured to provide downlink transmissions of a content signalaccording to a repetition pattern, and the ES scheme is configured tomodify or cancel the repetition pattern for downlink transmitting thecontent signal.
 5. The method of claim 1, wherein the wirelesscommunication system includes a frequency division duplex (FDD) systemand a time division duplex (TDD) system.
 6. The method of claim 5,wherein the ES scheme is configured to incorporate dynamic adjustmentsof uplink and downlink allocations in the TDD system.
 7. The method ofclaim 1, wherein the wireless communication system is a long termevolution (LTE) system.
 8. The method of claim 7, wherein the referencesignal is a cell-specific reference signal (CRS), the first region ofeach subframe is configured to carry a physical layer control channel(PDCCH), and the second region of each subframe is configured to carry aphysical layer shared channel (PDSCH).
 9. The method of claim 1, whereineach subframe comprises a plurality of symbols in a time domain, one ormore symbols in each frame carrying either a control signal or a contentsignal, and the reference signal is a type of control signal.
 10. Themethod of claim 7, wherein each subframe is at least one of a regularsubframe, a MBSFN subframe and a special subframe used in a TDD system.11. A method for reducing power consumption in downlink transmissions ofone or more frames in a wireless communication system, each framecomprising a plurality of subframes and each subframe divided into atleast a first region and a second region in a time domain, the methodcomprising: selecting a first group of subframes from the plurality ofsubframes, each of the first group of subframes having at least acontrol signal symbol in the first region; for each subframe notselected in the first group, disabling transmission of any controlsignal symbol in the first region; selecting a second group of subframesfrom the plurality of subframes, each of the second group of subframeshaving one or more control signal symbols in the second region; and foreach subframe not selected in the second group, disabling transmissionof any symbol in the second region unless the subframe carries aparticular content signal.
 12. The method of claim 11, wherein eachsubframe comprises a plurality of symbols in the time domain, eachsymbol configured for carrying a control signal or a content signal. 13.The method of claim 11, wherein the wireless communication system is along term evolution (LTE) system.
 14. The method of claim 13, whereinthe control signal symbol carries a cell-specific reference signal(CRS), the particular content signal is PCBH or SIB1, the first regionof each subframe is configured to carry a physical layer control channel(PDCCH), and the second region of each subframe is configured to carry aphysical layer shared channel (PDSCH).
 15. The method of claim 11,wherein the wireless communication system includes a FDD system and aTDD system.
 16. The method of claim 15, further comprising adjustinguplink and downlink allocations to further reduce the power consumptionin the TDD system.
 17. The method of claim 11, further comprisingreducing a repetition frequency in downlink transmissions of a contentsignal in the wireless communication system, the content signal having apredetermined frequency for updating the contents therein.
 18. Anapparatus for reducing power consumption in downlink transmissions ofone or more frames in a wireless communication system, each framecomprising a plurality of subframes and each subframe divided into atleast a first region and a second region in a time domain, the apparatuscomprising: means for selecting a first group of subframes from theplurality of subframes, each of the first group of subframes having atleast a control signal symbol in the first region; means for disablingtransmission of any control signal symbol in the first region of eachsubframe not selected in the first group; means for selecting a secondgroup of subframes from the plurality of subframes, each of the secondgroup of subframes having one or more control signal symbols in thesecond region; and means for disabling transmission of any symbol in thesecond region unless the subframe carries a particular content signal ineach subframe not selected in the second group.
 19. The apparatus ofclaim 18, further comprising means for reducing a repetition frequencyin downlink transmissions of a content signal in the wirelesscommunication system, the content signal having a predeterminedfrequency for updating the contents therein
 20. The apparatus of claim18, wherein the wireless communication system is an LTE system includingFDD and TDD systems.
 21. A computer program product for reducing powerconsumption in downlink transmissions of one or more frames in awireless communication system, wherein each frame comprises a pluralityof subframes and each subframe is divided into at least a first regionand a second region, the computer program product embodied incomputer-readable storage medium comprising instructions, whileexecuted, causing a computer to perform: selecting a first group ofsubframes from the plurality of subframes, each of the first group ofsubframes having at least a control signal symbol in the first region;for each subframe not selected in the first group, disablingtransmission of any control signal symbol in the first region; selectinga second group of subframes from the plurality of subframes, each of thesecond group of subframes having one or more control signal symbols inthe second region; and for each subframe not selected in the secondgroup, disabling transmission of any symbol in the second region unlessthe subframe carries a particular content signal.
 22. The computerprogram product of claim 21, incorporated in a base station in thewireless communication system.
 23. The computer program product of claim22, wherein the base station comprises a transmitter configured fordownlink transmissions of the frames, subframes and symbols, thetransmitter including a power amplifier (PA).
 24. A base station in awireless communication system, comprising: a transmitter configured fordownlink transmissions of a frame comprising a plurality of subframes,each subframe divided into at least a first region and a second region;a downlink signal processor coupled to the transmitter; and a controllercoupled to the downlink signal processor, the controller comprising apower reduction module configured to selectively disable downlinktransmissions of control signal symbols by: selecting a first group ofsubframes from a plurality of subframes, each of the first group ofsubframes having at least a control signal symbol in the first region;for each subframe not selected in the first group, disablingtransmission of any control signal symbol in the first region; selectinga second group of subframes from the plurality of subframes, each of thesecond group of subframes having one or more control signal symbols inthe second region; and for each subframe not selected in the secondgroup, disabling transmission of any symbol in the second region unlessthe subframe carries a particular content signal.
 25. The base stationof claim 24, wherein the transmitter is coupled to one or more poweramplifiers (PAs), and the PA-on time in each PA is reduced by the powerreduction module.
 26. The base station of claim 24, further comprising ascheduler coupled to the downlink signal processor, the scheduleconfigured to schedule downlink transmissions of each frame, subframeand symbols.
 27. The base station of claim 24, further comprising anantenna coupled to the transmitter, the antenna having one or moreports, each port coupled to a power amplifier.
 28. The base station ofclaim 24, further comprising an Input/Output (I/O) interface coupled tothe controller, the I/O interface configured to enable the base stationcommunicating with one or more networks.
 29. The base station of claim24, wherein the power reduction module is further configured forreducing a repetition frequency in downlink transmissions of a contentsignal in the wireless communication system, the content signal having apredetermined frequency for updating the contents therein.
 30. The basestation of claim 24, wherein the wireless communication system is an LTEsystem having FDD and TDD systems.